U.S. patent application number 16/199811 was filed with the patent office on 2020-05-28 for switchable and reconfigurable grating couplers.
The applicant listed for this patent is GLOBALFOUNDRIES Inc.. Invention is credited to Yusheng Bian, Ajey Poovannummoottil Jacob.
Application Number | 20200166709 16/199811 |
Document ID | / |
Family ID | 70771444 |
Filed Date | 2020-05-28 |
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United States Patent
Application |
20200166709 |
Kind Code |
A1 |
Bian; Yusheng ; et
al. |
May 28, 2020 |
SWITCHABLE AND RECONFIGURABLE GRATING COUPLERS
Abstract
Structures for a waveguide and methods of fabricating a
structure for a waveguide. A grating coupler is formed that has an
arrangement of grating structures. A conformal layer is arranged
over the plurality of grating structures. The conformal layer is
composed of a tunable material having a refractive index that
changes with an applied voltage.
Inventors: |
Bian; Yusheng; (Ballston
Lake, NY) ; Jacob; Ajey Poovannummoottil;
(Watervliet, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GLOBALFOUNDRIES Inc. |
Grand Cayman |
|
KY |
|
|
Family ID: |
70771444 |
Appl. No.: |
16/199811 |
Filed: |
November 26, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 2006/12176
20130101; G02B 5/1847 20130101; G02B 6/124 20130101; G02B 6/34
20130101; G02B 5/1828 20130101; G02B 2006/12061 20130101 |
International
Class: |
G02B 6/34 20060101
G02B006/34 |
Claims
1. A structure comprising: a grating coupler including a plurality
of grating structures; and a first conformal layer arranged over
the plurality of grating structures, the first conformal layer
comprised of a tunable material having a refractive index that
changes with an applied voltage.
2. The structure of claim 1 wherein the tunable material is
indium-tin oxide.
3. The structure of claim 1 wherein the tunable material is
indium-tin oxide, vanadium oxide, germanium-antimony telluride, or
a combination thereof.
4. The structure of claim 1 wherein the tunable material is an
electro-optic polymer or a liquid crystal.
5. The structure of claim 1 further comprising: a first contact
connected with the first conformal layer; and a second contact
connected with the plurality of grating structures.
6. The structure of claim 5 further comprising: a back-end-of-line
stack arranged over the first conformal layer and the plurality of
grating structures, wherein the first contact and the second
contact are coupled with the back-end-of-line stack.
7. The structure of claim 1 wherein the plurality of grating
structures are comprised of an electrical insulator.
8. The structure of claim 7 further comprising: a second conformal
layer arranged over the plurality of grating structures, the second
conformal layer comprised of a conductor; and a conformal
dielectric layer arranged between the first conformal layer and the
second conformal layer.
9. The structure of claim 7 wherein the electrical insulator is
silicon nitride.
10. The structure of claim 1 further comprising: a second conformal
layer arranged over the plurality of grating structures, the second
conformal layer comprised of a conductor; and a conformal
dielectric layer arranged between the first conformal layer and the
second conformal layer.
11. The structure of claim 1 wherein the plurality of grating
structures are comprised of a conductor.
12. The structure of claim 11 further comprising: a conformal
dielectric layer arranged between the first conformal layer and the
plurality of grating structures.
13. The structure of claim 11 wherein the conductor is a doped
polycrystalline semiconductor material.
14. The structure of claim 1 further comprising: a back-end-of-line
stack arranged over the grating coupler.
15. The structure of claim 14 further comprising: a dielectric
layer arranged over the back-end-of-line stack, the dielectric
layer comprised of silicon nitride.
16. A method comprising: forming a grating coupler having a
plurality of grating structures; and forming a first conformal
layer over the plurality of grating structures of the grating
coupler, wherein the first conformal layer is comprised of a
tunable material having a refractive index that changes with an
applied voltage.
17. The method of claim 16 further comprising: depositing a
conformal dielectric layer over the first conformal layer on the
plurality of grating structures; and depositing a second conformal
layer comprised of a conductor that is arranged over the conformal
dielectric layer on the plurality of grating structures, wherein
the plurality of grating structures are comprised of an electrical
insulator.
18. The method of claim 17 further comprising: forming a first
contact connected with the first conformal layer; forming a second
contact connected with the second conformal layer; and forming a
back-end-of-line stack arranged over the grating coupler, wherein
the first contact and the second contact are each connected with
wiring in the back-end-of-line stack.
19. The method of claim 16 further comprising: depositing at least
one conformal dielectric layer arranged over the plurality of
grating structures and between the first conformal layer and the
plurality of grating structures, wherein the plurality of grating
structures are comprised of a conductor.
20. The method of claim 19 further comprising: forming a first
contact connected with the first conformal layer; forming a second
contact connected with the plurality of grating structures; and
forming a back-end-of-line stack arranged over the grating coupler,
wherein the first contact and the second contact are each connected
with wiring in the back-end-of-line stack.
Description
BACKGROUND
[0001] The present invention relates to photonics chips and, more
specifically, to structures for a grating coupler and methods of
fabricating a structure for a grating coupler.
[0002] Photonics chips are used in many applications and systems
including, but not limited to, data communication systems and data
computation systems. A photonics chip integrates optical
components, such as waveguides and bends, and electronic
components, such as field-effect transistors, into a unified
platform. Among other factors, layout area, cost, and operational
overhead may be reduced by the integration of both types of
components.
[0003] Grating couplers are commonly used in photonics chips for
coupling optical signals between waveguides and optical fibers. In
general, grating couplers are fixed optical elements having an
optical performance that cannot be tuned, switched, or
configured.
[0004] Improved structures for a grating coupler and methods of
fabricating a structure for a grating coupler are needed.
SUMMARY
[0005] In an embodiment of the invention, a structure includes a
grating coupler having a plurality of grating structures and a
conformal layer arranged over the plurality of grating structures.
The conformal layer is composed of a tunable material having a
refractive index that changes with an applied voltage.
[0006] In an embodiment of the invention, a method includes forming
a plurality of grating structures of a grating coupler, and forming
a conformal layer over the plurality of grating structures of the
grating coupler. The conformal layer is comprised of a tunable
material having a refractive index that changes with an applied
voltage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate various
embodiments of the invention and, together with a general
description of the invention given above and the detailed
description of the embodiments given below, serve to explain the
embodiments of the invention. In the drawings, like reference
numerals refer to like features in the various views.
[0008] FIG. 1 is a top view of a photonics chip including a
structure at an initial fabrication stage of a processing method in
accordance with embodiments of the invention.
[0009] FIG. 2 is a cross-sectional view of the structure taken
generally along line 2-2 in FIG. 1.
[0010] FIG. 2A is a cross-sectional view of a structure in
accordance with alternative embodiments of the invention.
[0011] FIGS. 3-5 are cross-sectional views of the structure at
successive fabrication stages subsequent to FIG. 2.
DETAILED DESCRIPTION
[0012] With reference to FIGS. 1, 2 and in accordance with
embodiments of the invention, a structure 10 includes a grating
coupler 12 arranged over a semiconductor layer 14 and a waveguide
16 that is coupled with the grating coupler 12. A dielectric layer
17 composed of a dielectric material, such as silicon dioxide, may
be arranged between the grating coupler 12 and the semiconductor
layer 14. The semiconductor layer 14 may be composed of a
single-crystal semiconductor material, such as single-crystal
silicon from a device layer of a silicon-on-insulator (SOI) wafer.
The silicon-on-insulator (SOI) wafer further includes a buried
insulator layer 13 composed of a dielectric material, such as
silicon dioxide, and a substrate 15 composed of a semiconductor
material. The waveguide 16 provides optical signals to the grating
coupler 12.
[0013] The grating coupler 12 includes an arrangement of grating
structures 18 defined in a layer, generally indicated by reference
numeral 20, by notches or grooves 22. The grooves 22 are formed in
the layer 20 by lithography and etching processes. In the
representative embodiment, the grooves 22 extend partially through
the layer 20 such that the grating structures 18 are connected with
each other by a thin web 19 of the layer 20 that is located within
the grooves 22 over the dielectric layer 17. The grooves 22 are
trenches that define respective spaces or gaps arranged between
adjacent pairs of the grating structures 18. In an embodiment, the
grating structures 18 and grooves 22 may be arranged as a group of
spaced-apart parallel lines having given dimensions (e.g., width,
w, and length). In an alternative embodiment, the grating
structures 18 and grooves 22 may be arranged as a group of
concentric arcs that are nested together and that have given
dimensions (e.g., width and arc length).
[0014] The grating structures 18 and grooves 22 may have a given
periodicity defined by a pitch and a filling factor or duty cycle
relating to their dimensions. The pitch represents a distance in a
horizontal direction between adjacent pairs of the grating
structures 18, and the duty cycle represents a fraction of the area
of the grating coupler 12 that is occupied by the grating
structures 18. In an alternative embodiment, the grating structures
18 of the grating coupler 12 may be apodized (i.e., aperiodic) with
a pitch that varies as a function of position (i.e., location along
the z-axis).
[0015] The grooves 22 may be formed in the layer 20 by lithography
and etching processes that applies an etch mask formed by a
lithography process over the deposited layer 20 and that etches the
masked layer 20 with an etching process, such as reactive ion
etching (ME). The etching process may be selected to stop on the
material of the dielectric layer 17 after penetrating fully through
the layer 20. In an embodiment, the grating structures 18 may be
composed of a doped polycrystalline semiconductor material, such as
doped polysilicon, that is deposited by chemical vapor
deposition.
[0016] In an alternative embodiment and as shown in FIG. 2A, the
etching process may extend the grooves 22 fully through the layer
20 such that the grating structures 18 are disconnected from each
other. The etching process may be selected to stop on the material
of the dielectric layer 17 after penetrating fully through the
layer 20. In an alternative embodiment and as also shown in FIG.
2A, the semiconductor layer 14 may be patterned to form grooves
that match the pitch and duty cycle of the grating structures 18
and grooves 22, and that are filled by the dielectric material of
the dielectric layer 17.
[0017] In the representative embodiment, the grating structures 18
are depicted as rectangular shapes having vertical sidewalls.
However, in alternative embodiments, the grating structures 18 may
be trapezoidal with sidewalls tapering from top to bottom,
trapezoidal with sidewalls having inverse tapering (i.e., flaring)
from top to bottom, or non-rectangular (e.g., rounded
sidewalls).
[0018] With reference to FIG. 3 in which like reference numerals
refer to like features in FIG. 2 and at a subsequent fabrication
stage, conformal dielectric layers 24, 26 composed of respective
dielectric materials are sequentially formed by, for example,
atomic layer deposition over the grating structures 18. The
conformal dielectric layer 24 may be composed of an oxide of
silicon (e.g., silicon dioxide) or an oxide of hafnium (e.g.,
hafnium oxide), and the conformal dielectric layer 26 may be
composed of silicon nitride. The conformal dielectric layer 24 may
be in direct contact with the exterior surfaces of the grating
structures 18 and the web 19 of the layer 20, and the conformal
dielectric layer 26 may be in direct contact with the conformal
dielectric layer 24. The grating structures 18 are encapsulated or
encased inside of the conformal dielectric layer 24 and the
dielectric layer 17 with the conformal dielectric layer 26
providing an overlay extending across the encapsulated grating
structures 18. As used herein, a layer that is conformal may be
characterized by a substantially uniform thickness that conforms to
any underlying topography.
[0019] A tunable material layer 30 is formed over the conformal
dielectric layer 26, and may be formed in direct contact with the
conformal dielectric layer 26 over the grating structures 18 and
the web 19 of the layer 20. The tunable material layer 30 may be
composed of a tunable material deposited as a conformal layer by
atomic layer deposition or chemical vapor deposition. In an
embodiment, the tunable material layer 30 may be composed of a
conductor that is a tunable material by an applied bias voltage. In
an embodiment, the tunable material layer 30 may be composed of
indium-tin oxide (ITO). In an embodiment, the tunable material
layer 30 may be composed of other types of inorganic tunable
materials, such as vanadium oxide and germanium-antimony telluride,
or a combination of one or both of these materials with indium-tin
oxide. In an embodiment, the tunable material layer 30 may be
composed of an electro-optic polymer or liquid crystal.
[0020] The ability to tune the tunable material of the arises from
material properties of the tunable material layer 30 that provide a
permittivity (i.e., dielectric constant) that can be varied by an
applied bias voltage. The refractive index of the tunable material
layer 30 is related to the permittivity and, for that reason, the
refractive index of the tunable material layer 30 is also a
function of a bias voltage applied to the tunable material layer
30. The refractive index of the tunable material layer 30 can be
varied with the applied bias voltage to effectively switch the
grating coupler 12 between different states for transmitting
optical signals at a given wavelength. In one state (e.g., no
applied bias voltage), the tunable material layer 30 may have a
high refractive index and exhibit low optical signal absorption
such that the grating coupler 12 has its transmission spectrum
characterized by a peak wavelength with optimum coupling
efficiency. In another state (e.g., an applied negative bias
voltage), the tunable material layer 30 may have a high refractive
index and exhibit low optical signal absorption such that the
grating coupler 12 has its transmission spectrum characterized by a
different peak wavelength with optimum coupling efficiency. For
example, the peak wavelength for optimum coupling efficiency may be
shifted by 10 nanometers to 50 nanometers between the two different
states.
[0021] The conformal dielectric layers 24, 26 are composed of
respective electrical insulators (i.e., dielectric materials) that
are disposed between the grating structures 18 and the tunable
material layer 30. In an alternative embodiment, the conformal
dielectric layer 26 may be omitted from the structure 10 such that
the tunable material layer 30 is in direct contact with the
conformal dielectric layer 24.
[0022] With reference to FIG. 4 in which like reference numerals
refer to like features in FIG. 3 and at a subsequent fabrication
stage, a dielectric layer 28 is formed over the grating coupler 12
and the tunable material layer 30. The dielectric layer 28 may have
a thickness that is greater than the height of the grating
structures 18 such that the grating coupler 12 is buried in the
dielectric material of the dielectric layer 28. The dielectric
layer 28 may be composed of a dielectric material, such as an oxide
of silicon, deposited by chemical vapor deposition and planarized
with, for example, chemical mechanical polishing (CMP). For
example, the dielectric layer 28 may be composed of silicon dioxide
deposited by chemical vapor deposition using ozone and
tetraethylorthosilicate (TEOS) as reactants.
[0023] A multilayer back-end-of-line stack, generally indicated by
reference numeral 32, is formed by back-end-of-line (BEOL)
processing over the dielectric layer 28. The back-end-of-line stack
32 may include one or more interlayer dielectric layers composed of
one or more dielectric materials, such as a carbon-doped silicon
oxide, and metallization composed of, for example, copper,
tungsten, and/or cobalt that is arranged in the one or more
interlayer dielectric layers. An optional cladding layer 34
composed of a dielectric material, such as silicon nitride, may be
deposited over the back-end-of-line stack 32.
[0024] A contact 40 may be formed that connects the tunable
material layer 30 with wiring in the back-end-of-line stack 32, and
a contact 41 may be formed that connects the grating structures 18
with wiring in the back-end-of-line stack 32. The contacts 40, 41
may be composed of a metal, such as tungsten, copper, or cobalt,
and are located in respective etched contact openings. Through
these connections, a switchable bias voltage may be applied from
the wiring in the back-end-of-line stack 32 to the grating
structures 18 and the tunable material layer 30.
[0025] The grating coupler 12 may be tunable with an adjustable
and/or switchable coupling efficiency and a reconfigurable
transmission spectrum. To that end, the tunable material layer 30
and the grating structures 18 are connected to a switchable bias
voltage, which may be supplied from the wiring in the
back-end-of-line stack 32. As discussed hereinabove, the bias
voltage changes the permittivity and refractive index of the
tunable material layer 30 such that the peak wavelength in the
transmission spectrum of the grating coupler 12 is adjustable and
configurable.
[0026] The tunable material layer 30 functions simultaneously as an
optical layer that tunes the transmission/reflection of the grating
coupler performance, and as an electrode to enable connection with
metal contacts, which are used for applying voltages and enabling
tunability. The ability to enable tunable coupling efficiency and a
reconfigurable transmission spectrum may permit a single device
structure to operate with optimal coupling efficiencies at
different wavelengths and/or be used to compensate for a possible
wavelength shift induced by fabrication imperfections. The ability
to shift the wavelength transmitted through the grating coupler 12
may permit a single device structure to be used on photonics chips
in which the optical components handle multiple wavelengths, such
as in association with wavelength-division multiplexing.
[0027] The structure 10, in any of its embodiments described
herein, may be integrated into a photonics chip 50 (FIG. 1) that
includes electronic components 52 and additional optical components
54. For example, the electronic components 52 may include
field-effect transistors that are fabricated by CMOS
front-end-of-line (FEOL) processing.
[0028] With reference to FIG. 5 in which like reference numerals
refer to like features in FIG. 2 and in accordance with alternative
embodiments of the invention, the structure 10 may be modified to
form grating features 18a of the grating coupler 12 from a
different material. In an embodiment, the grating features 18a may
be composed of a dielectric material, such as silicon nitride.
Otherwise, the grating features 18a may have the same arrangement
as the grating features 18a. A waveguide 16a, which provides
optical signals to the grating coupler 12, is composed of the same
material as the grating features 18a. The grating coupler 12 may be
formed over a dielectric layer 42 composed of, for example, silicon
dioxide, instead of being formed over the semiconductor layer 14,
and an additional dielectric layer 44 composed of, for example,
silicon nitride may be formed between the grating coupler 12 and
the dielectric layer 42.
[0029] A conformal layer 36 composed of a conductor, such as a
doped polycrystalline semiconductor material (i.e., doped
polysilicon), may be deposited over the grating features 18a before
forming the conformal dielectric layer 24, and the conformal
dielectric layer 26 may be omitted. The conformal layer 36 may be
arranged in direct contact with the exterior surfaces of the
grating features 18a. The tunable material layer 30 and the
conformal layer 36 are connected with the switchable source of bias
voltage. Specifically, the contact 40 may connect the tunable
material layer 30 with wiring in the back-end-of-line stack 32, and
the contact 41 may connect the conformal layer 36 with wiring in
the back-end-of-line stack 32.
[0030] The methods as described above are used in the fabrication
of integrated circuit chips. The resulting integrated circuit chips
can be distributed by the fabricator in raw wafer form (e.g., as a
single wafer that has multiple unpackaged chips), as a bare die, or
in a packaged form. The chip may be integrated with other chips,
discrete circuit elements, and/or other signal processing devices
as part of either an intermediate product or an end product. The
end product can be any product that includes integrated circuit
chips, such as computer products having a central processor or
smartphones.
[0031] References herein to terms modified by language of
approximation, such as "about", "approximately", and
"substantially", are not to be limited to the precise value
specified. The language of approximation may correspond to the
precision of an instrument used to measure the value and, unless
otherwise dependent on the precision of the instrument, may
indicate +/-10% of the stated value(s).
[0032] References herein to terms such as "vertical", "horizontal",
etc. are made by way of example, and not by way of limitation, to
establish a frame of reference. The term "horizontal" as used
herein is defined as a plane parallel to a conventional plane of a
semiconductor substrate, regardless of its actual three-dimensional
spatial orientation. The terms "vertical" and "normal" refer to a
direction perpendicular to the horizontal, as just defined. The
term "lateral" refers to a direction within the horizontal
plane.
[0033] A feature "connected" or "coupled" to or with another
feature may be directly connected or coupled to or with the other
feature or, instead, one or more intervening features may be
present. A feature may be "directly connected" or "directly
coupled" to or with another feature if intervening features are
absent. A feature may be "indirectly connected" or "indirectly
coupled" to or with another feature if at least one intervening
feature is present. A feature "on" or "contacting" another feature
may be directly on or in direct contact with the other feature or,
instead, one or more intervening features may be present. A feature
may be "directly on" or in "direct contact" with another feature if
intervening features are absent. A feature may be "indirectly on"
or in "indirect contact" with another feature if at least one
intervening feature is present.
[0034] The descriptions of the various embodiments of the present
invention have been presented for purposes of illustration, but are
not intended to be exhaustive or limited to the embodiments
disclosed. Many modifications and variations will be apparent to
those of ordinary skill in the art without departing from the scope
and spirit of the described embodiments. The terminology used
herein was chosen to best explain the principles of the
embodiments, the practical application or technical improvement
over technologies found in the marketplace, or to enable others of
ordinary skill in the art to understand the embodiments disclosed
herein.
* * * * *